Results of the current study revealed that a lectin extracted from Polygonum persicaria L. had significant inhibition on digestive α-amylase of Chilo suppressalis Walker. Concentrations 0.05 to 2 mg/ml of PPA significantly decreased enzymatic activity from 5 to 72%. The highest inhibition of α-amylase was obtained at pH 9 while the optimal pH for amylolytic activity was found to be 8 and 9. Besides, optimal temperature of α-amylase activity was at 30ËC but the highest inhibition of the enzyme was found at temperatures of 30-40ËC. Kinetic parameters of α-amylase revealed lower and higher amounts of Vmax and Km in PPA treated enzyme indicating mixed inhibition. In vitro inhibition of α-amylase clearly showed that PPA could intervene in digestive process of C. suppressalis and decrease nutrient income of larvae. Further experiments are required to fully understand negative effects of PPA against rice striped stem borer to reach an efficient pest control via providing resistant varieties.